Pleural drainage devices which are used to maintain the appropriate suction level within the pleural cavity of a patient are well-known. The first unitary device developed for collecting fluids from the pleural cavity and controlling the suction level within the pleural cavity is disclosed in U.S. Pat. No. 3,363,626. This apparatus provides three chambers, one chamber comprising a collection chamber for collecting the fluids drained from the pleural cavity through a thoracotomy tube, a second chamber known as an underwater seal chamber which protects the pleural cavity from being subject to atmospheric pressure, and a third chamber known as a pressure manometer chamber which serves to regulate the degree of negative pressure within the pleural cavity. This type of apparatus has been highly successful in both removing fluids from the pleural cavity and in maintaining the desired degree of negativity within the pleural cavity.
However, the apparatus disclosed in U.S. Pat. No. 3,363,626 required prefilling of an underwater seal chamber with water as well as prefilling of the manometer chamber to the desired level to maintain the desired degree of negativity within the pleural cavity. U.S. Pat. No. 4,605,400 discloses a pleural drainage apparatus which eliminates the underwater seal chamber and the water filled manometer chamber to regulate the degree of suction. This patent discloses the use of one-way valves which perform the function of preventing atmospheric air from entering the collection chamber and separate one-way valves which open to admit atmospheric air to the passageway between the collection chamber and the suction source to maintain the desired degree of negativity within the collection chamber.
In practice, it has been found that the suction level from the suction source in a hospital varies over a wide range dependent upon the degree of use of the suction available. Under these circumstances, it is difficult to maintain the desired degree of negativity within the collection chamber and the patient's pleural cavity with any precise degree of accuracy. While the valve means disposed within the pleural cavity shown in U.S. Pat. No. 4,605,400 can maintain the degree of negativity at an appropriate level when the suction source is providing suction within a normal range, when a very high degree of suction is provided by the suction source, the valves cannot provide sufficient air flow to maintain the desired degree of negativity.